Core Memory Explained and Demonstrated 

Genius! As a self-actualising geek, that would definitely have been a cherished memory! Thank you for sharing 🙂

Fascinating!! Are there any links to such a device to see the guts of it?

I bet that was horrendously expensive when made.

@@Lucianrider Looks like somone did video of it this year. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-tPT6nIRFI_I.html. I am sure when they sold it it was expensive, but parts wise there wasn't much to it. Basically a counter and hard switch over buttons and you just thread the wire in or over magnets.

Look mum no computer has one in his collection! Check out his videos!

And think 100 years from now (if we are not extinct) they will look at our state of the art computer science and hardware, with the same view as we look at this. No doubt humans then will be wondering how we ever managed with things so archaic,

And there it is. The first dad joke of the thread :)

"Dad joke?" Well, maybe a bit... @@TrainDriver186

@@dapje2002 Thanks for the compliment. I really dig it.

@@TrainDriver186 Stubby beat me to it. I have to go take a nap now...

HA!

Peter Švančárek - The man was An Wang, although others contributed ideas pertaining to the organization of the cores.

Had to keep running a schmoo plot on ours as it would not keep running, finally found a cracked resistor in the termination of one of the 2 drive lines. Sense was OK. The current would not stay stable with a bad resistor. Took a couple weeks to find due to issues of opening the oven and waiting for it to stabilize each time. If you worked on these, it was one of the resistors on the end of the row and column drive lines. Sure felt good finding the root cause after so much time spent adjusting and re-adjusting the row and column drive currents to get the schmoo plot correct. This was in the late 1970's.

Forgot to mention the curve he shows in the graphic is actually the Hysteresis curve of the magnetic core. That shows the ability for the core to remain magnetized after the current stops. The Schmoo curve is the boundary of where a current does not change the core magnetization and where it "flips the bit" Since there is an X and Y wire through the core, one axis of the Schmoo is the x current and the Y current to flip the bit. Inside all bits flip where X and Y currents add. As X and or Y is changed, some bits start to fail to flip when addressed. The middle of the all bits flip zone is the high reliability zone and X and Y currents are set there for Writing and Reading. The 3 wires are the X and Y. In one polarity they add and Write a bit. The 3rd wire that is weaved through all bits, is the sense. It senses the bit did or did not flip. The read cycle is done by writing the bits in a row to zero one at a time. If the bit was a 1 the sense will detect the flip. then the row is written back as a read only erases the memory. Kind of brief, but a rundown of how it works. This point where it will flip is affected by temperature, so they are kept in a temperature controlled oven for reliability. Core memory was often operated at about 120-150F.

worth noting, that the radiation aspect is usually widly exaggerated.

@@Thisandthat8908 Depends on where you are. There are certain areas in orbit where the radiation is extremely high, and does cause reliability issues with non-radiation hardened circuitry.

aaa yep that makes sense now :D

Ahhh, a fellow Bitburger!! I was there 86-88. Miss that place!!

I was at holloman in 77. Grew up in alamo. I miss those f 4 flying over head low and loud! The sound of freedom.

@@improvesynthsational8466 , I liked Alamagordo, and had a pretty good time there, even if it did get hot as heck in the Summer.

That's what you get for allowing Frenchmen into the country.

somewhat oddly, some units in the US have moved to a 10 based system, but with a "mil" being a 0.001 inches. I've encountered tape measures for surveying with feet divided by 10. Though at some point its just starts getting weird.

those caveman freedom units put a man on the moon 50 years ago! but we're not evolved.. lol

@@paulkaygmailcom That's always going to be my argument for the US Standard and Imperial systems not being inferior.

@@bryceforsyth8521 They may have put people on the moon. But what is more complicated: Converting from miles to inches (what is the right multiplicator?) or from kilometers to centimeters (just shift that decimal place over)? You can *measure* anything in either system, but the convenience factor when *working* with those measurements is clearly on the metric side. ;-)

"walk down memory lane" >_>

yeah but it was non volatile

True it was a big improvement over those old technologies. Modern multi level cell NAND flash is arguably even crazier than core under the hood with several bits being stored per cell as varying charge levels, error correction, and wear leveling algorithms being used.

*than

Ah. Yea, I guess I shoudl read what I type. Or mayeb should. Ir maybe should. Or maybe should. I have distypeia. :-) (And yes, every one of those was an accidental typo.)

"The hard *core* way"...

I am a metric “native”. But the US was dominating the early computer industry and the cores were specified and manufactured in round number of mils.

@@CuriousMarc Understood. Hopefully metric will take over in the US given enough time. I'm always confused when visiting Britain and seeing the MPH speed and distance and everything else metric. Maybe it's something with speaking English...

..I mean... wire is measured in mils too so... it stands to reason

@ClickThisToSubscribe A centimetre is not arbitrary. It's part of a system where everything ties together. For example 1 cubic centimetre is the same volume as 1 millilitre and (water) weighs 1 gram and takes 1 calorie to increase the temperature by 1° C. Now try that with inches, ounces, pints (Imperial or American?), BTU and ° F.

@Non,Player, Adeptus ???? No, it's not arbitrary. It's a system where the various measures are tied together in a coherent manner. On the other hand, the imperial system is very arbitrary, with the measures based on something that might have made sense, but have nothing in relation to the others. You even have situations where the same unit has different sizes, such as imperial and U.S. gallon. Also, while an imperial quart has 5/4s the number of ounces of the U.S. quart, the actual volume difference is 6/5, because of the different size ounce. There are many other inconsistencies in the Imperial system(?).

If you look into the alternatives it replaced, you will find thornier engineering problems and often higher cost as well. Williams-Kilburn tubes used a modified cathode ray tube, where the face of the tube was a capacitor and the electron beam deposited charge at various spots in a grid across the face to represent bits. The electrons striking the inside of the CRT face would splash off in a fountain, contaminating nearby spots. The charge would drain off, too, requiring regular refreshing of the bit pattern. Programmers had to hop around with the bits they accessed as too much locality of reference produced excessive cumulative spray onto adjacent bits. These also require many kilovolts to drive the beam yet the detected pulse when reading was down in the microvolt range, requiring enormous amplification; cumulative noise was a big big problem in the amplifier chain. Mercury vat delay lines used acoustic signals that traveled through mercury. They had to be heated to a constant temperature to work. Reflections off the side walls of the tube would smear out the pulses, making reliable detection quite hard to accomplish. These, like the tubes above, took nearly continuous fiddling to achieve acceptable results. Drum memories required many read/write heads to get decent capacity. The memory was not random access, instead the program should keep track of the current rotational position of the drum so that the needed next memory word doesn't require any substantial portion of a rotation time to come back under the heads. These are both expensive and slow, limiting processor speed.

Reminds me of the Apple II that I had with 48K RAM.. did payroll in BASIC using a 360K floppy disk.. 1983. maxed that sucker out, had to watch the array size.. print out was by disk saved files.

I just have built Jussi Kilpeläinen's Core Memory Shield for the Arduino. When not connected to the Arduino but powered anyway, the enable signal is always on and current flows through one row and one column wire constantly. I noticed some related components and my makeshift 3.3V power supply heating up due to this constant current flow. I estimated the currents from the schematic and found a value of roughly 300 mA for the row and column current. Then I started to look for a confirmation of this estimation online. This video is one of the very few sources about core memory that makes comprehensive quantitative statements on the matter. And it explains the matter just beautifully with experiments. Well done, as always from CuriousMarc.

It depends on the size of the cores, and one of the reasons they kept making them smaller.

Not yet. Rope is even more complicated. However Ken made a great article to explain it, on his blog at www.righto.com/2019/07/software-woven-into-wire-core-rope-and.html

They used core on AP-101B since it was more proven at the time and was more resistant to cosmic rays. It shared it's architecture with the IBM 360 mainframe and was still was reasonably fast for the time maybe a little under 2x the performance of an IBM 5150. The APA-101S went to solid state memory and was half the size and weight.

@@Membrane556Yes quite true, would be interesting if any of AP-101B units are still in service anywhere!

@@nzoomed I think the air force still uses derivative of the 4pi in a couple of applications.

@@Membrane556 Does not surprise me considering they are still using 8 inch floppy disks to launch missiles!